1. Field of the Invention
The present invention relates to copolymers formed from N-(halogenated maleimide) monomers, (also called: "halogen and perhalo-organo substituted N-phenyl(or biphenyl) maleide monomers") and optical materials formed from the copolymers. The invention also relates to methods of making and using such copolymers and materials.
2. Description of Related Art
The micro-electronic and optical industries rely on hundreds of polymeric materials. Polymeric materials currently play an important role, for Example, as coating materials, as photonic devices, as electro-optical devices, and in packaging, such as for optical adhesives.
Passive optical polymers are non-field (electrical, magnetic and optical) response materials. These kinds of material have been used to fabricate various optical circuits for interconnections and switches. For Example, Dupont (B. L. Booth, "Polymers for Integrated Optical Waveguides", Polymers for Electronic and Photonic Application, (C. P. Wong, ed.), Academic Press, 1993) demonstrated a simple manufacture process to produce complicated power splitters and couplers by use of a mixture of acrylate monomers and oligomers. NORTEL (J. P. D. Cook, Applied Optics, 37, 1220 (1998)) fabricated stable polymer waveguides and micromirrors with halogenated acrylates by a UV curing process. NTT (Y. Hida, et al. IEEE Phot. Techn. Lett., 5, 782 (1993)) has shown the possibility of fabricating a thermooptical switching and a Mach-Zehnder interferometer from fluoromethacrylate, with much lower driving voltages and several mili-seconds scale of switching time. ETRIK (M. C. Oh., et al., Applied Physics Letters, 73, 2543 (1998)) described fabrication of a tunable wavelength filter with fiber bragg grating in polymer waveguides of fluorinated poly(arylene ethers).
Passive optical polymer materials, such as optical waveguides and couplers, often require very low optical loss of 0.1 dB/cm to 0.3 dB/cm at 1300 nm and 1550 nm. To reach this requirement is a very challenging objective for polymeric materials, because the key building blocks of polymers are carbon and hydrogen, which have a very strong overtone absorption from the C--H stretch vibration at the near IR region. Therefore, to reach this desired optical loss, materials often need to be halogenated at a very high level, to dilute the C--H bond. For Example, acrylate formulations often need at least 90% fluorination for 1550 nm and at least 55% fluorination for 1300 nm.
Besides the optical transparency, passive optical materials often have to meet very strict thermal (such as low coefficient of thermal expansion (CTE) and desired glass transition temperature (Tg) and mechanical (such as certain strength and flexibility) property requirements. The optical polymers generally also require completely amorphous structures to minimize optical scattering and birefringence.
For a better in-situ microstructure formation in devices and packaging, the monomers used to form the optical polymers are preferred to be ultraviolet (UV) or electron beam (EB) thermal curable in a short time. Fluorinated acrylates have been reported for passive optical devices, such as optical waveguides and couplers. See Eldada et al., "Sol-Gel and Polymer Photonic Devices", CR68, SPIE Press, 1997. A problem of these acrylates is their low glass temperature upon reaching a high degree of fluorination. Also the vinyl addition polymerization of acrylates yields a polymer with at least 3 hydrogens (CH.sub.2 =CHR) per repeat unit.
There also should be one or two CH.sub.2 spacer groups between the acrylate ester oxygen and the fluorocarbon chain to stabilize the ester bond against hydrolysis. Finally, in order to form a process-compatible amorphous polyacrylate, the maximum fluorination from linear fluorinated alcohol is eight CF.sub.2 units. Therefore, the structure of acrylates push the minimal optical loss to a higher level due to the overtone absorption of the five to seven CH bonds in each repeat unit. In order to have a 0.1 dB/cm optical loss at 1300 nm, full deuteration to replace the CH group is necessary. See A. Matsumoto, et al., Macromolecules 23, 4508 (1990). This comes with a high cost.
With the increasing fluorination on the side chain ester group, the glass transition temperature of fluorinated acrylate polymers decreases remarkably. Therefore, heavily fluorinated linear acrylate resins have difficulty meeting the 85% RH/85.degree. C. test. This test involves subjecting a waveguide material to 85.degree. C./85% RH conditions as in the standard Bellcore test (GR-1209-CORE, Issue 1, 1994), which is entitled "Generic Requirements for Fiber Optic Branching Components."
El-Guweri et al, "Partially Fluorinated Maleimide Copolymer for Langmuir Films of Improved Stability, Macromol. Chem. Phys., 198(2) 401-418 (1997) and Hendlinger et al., "Partially Fluorinated Maleimide Copolymers for Langmuir Films of Improved Stability", Langmuir, 13(2), 310-319, 1997, describe certain maleimide copolymers for Langmuir films. The fluorinated maleimides were copolymerized with styrene and vinyl ether to prove the concept of enhancement of the thermal stability of LB films. In these papers, two fluorinated vinyl ethers (1-trifluoromethyl-3-(2-vinyloxyethoxy)benzene and 1,2,3,4,5-pentafluoro-6-(2-vinyloxyethoxy)benzene) were used.
Dorr et al., "Reactions on Vinyl Isocyanate/Maleimide Copolymers:", Macromolecules, 31(5) 1454-1465 (1998) describes maleimide copolymers. However, these copolymers are disadvantageous because the fluorinated maleimide/vinyl isocyanate copolymer is not very useful as a waveguide material due to the high optical loss and hydrolysis properties of the hydrocarbon isocyanate group. In Dorr, the isocyanate group is intentionally incorporated into the polymer chain to perform a further attachment reaction with hydroxyl ended chromophores for non-linear optical application.
Hagiwara et al, "Polymerization of N-(2,3,4,5,6-pentafluorophenyl) maleimide), Macromol. Rapid Chem. Commun, 18(4), 303-311 (1997), describes homopolymers of the entitled monomers. Such homopolymers often do not provide the desired optical properties. Moreover the low molecular weight and poor film properties of this homopolymer, mean it can not be favorably used in microstructure manufacturing processes.